1. Field of the Invention
This invention relates to the preparation of novel metal compounds, particularly molybdenum compounds, based on a reaction of a metal source with hindered amines, and their incorporation into lubricant compositions containing a hindered amine and/or an aromatic amine.
2. Description of the Related Art
Oxidation is a major cause of the breakdown of lubricants. This results in a shortened lifespan of the lubricant, requiring more frequent changes, especially in demanding environments such as internal combustion engines.
Antioxidants have therefore played an important role as additives in lubricants in order to extend their useful life. Aromatic amines, especially secondary diarylamines, e.g., alkylated diphenylamines, phenothiazines, and alkylated N-naphthyl-N-phenylamines have been important additives to lubricating compositions. Also important have been phenolic compounds in retarding oxidation.
Other antioxidants have also been used. U.S. Pat. Nos. 5,073,278 and 5,273,669 to Schumacher et al. disclose the use of hindered amines in a lubricating oil. U.S. Pat. No. 5,268,113 to Evans et al. discloses the synergistic combination of a hindered amine with phenolic compounds.
Oil-soluble molydenum compounds are also known to provide antioxidant capabilities in lubricant compositions. U.S. Pat. No. 4,122,033 to Black discloses an oxidation inhibitor for lubricating oils that one or more transition metal containing compounds can be utilized in as oxidation inhibitors in lubricating compositions. Among the transition metal compounds useful are the salts of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, tellurium, ruthenium, rhodium, palladium, and silver. It was also found in U.S. Pat. No. 4,705,641 to Goldblatt et al., that the combination of copper and molybdenum salts were effective as antioxidants in lubricant compositions. However, in both patents antioxidant activity was only found under certain conditions.
The combination of an antioxidant with a metal compound has been important in the extending the lifetime of the antioxidant. For example, U.S. Pat. No. 5,994,277 to Richie et al. teaches that a crankcase lubricant composition which contains copper, molybdenum and aromatic amines can act as an effective antioxidant combination. U.S. Pat. No. 6,306,802 to Shaub et al. discloses sulfurized molybdenum complexes with oil-soluble aromatic amines. Gatto, et al., in U.S. Pat. No. RE38,929E has disclosed the combination of certain sulfur and phosphorus-free molybdenum compounds and secondary diarylamines improved the useful life of a lubricating oil. The most effective amounts in inhibiting oxidation were between 100 and 450 parts per million (ppm) of molybdenum, and between 750 and 5,000 ppm of an oil-soluble secondary diphenylamine.
Oil-soluble molybdenum compounds are also known to provide antifriction properties to a lubricant composition. Friction is of particular significance in internal combustion engines, because loss of substantial amount of theoretical mileage is traceable directly to friction. Friction will increase the power required to effect movement, thus increasing fuel consumption. Therefore, it is advantageous to use lubricants which minimize this friction.
Since various antifriction additives act in a different physical or chemical manner, only some satisfy the effectiveness and compatibility criteria leading to a significant energy loss prevention function of the lubricant. Types of molybdenum compounds known to be useful in engine lubricants include certain dithiocarbamate derivatives of molybdenum disclosed in U.S. Pat. No. 4,259,254. The use of molybdenum complexes of fatty alkyl amines in conjunction with a sulfur donor is taught in U.S. Pat. No. 4,164,473.
It has been surprisingly discovered that novel oil-soluble molybdenum compounds prepared from hindered amines impart unusually strong antioxidant and excellent antifriction properties to lubricants, potentially resulting in longer lubricant lifetime, and improved fuel economy. The antioxidant activity far exceeds other molybdenum complexes under the same testing conditions. We have also discovered that lubricant compositions containing the novel molybdenum compounds either alone, or in combination with a hindered amine and/or a secondary diarylamine can give enhanced antioxidant protection to that lubricant.